1. Field of the Invention
The disclosure herein relates generally to methods for determining the composition of a material sample by analyzing electromagnetic energy that has been passed through or emitted from the material sample.
2. Description of the Related Art
A large number of people suffer from diabetes and other conditions in which the natural regulation of blood glucose levels is impaired. For these people, monitoring blood glucose level is an important part of health maintenance, and a variety of techniques and instruments have been developed to periodically measure glucose levels in blood samples for this purpose.
Most of these methods involve a spectroscopic measurement, where the absorption of electromagnetic energy of a blood sample is measured and correlated to glucose concentration. In some cases, the electromagnetic energy is at optical wavelengths. In these systems, a chemical reagent is typically added to the blood sample which chemically reacts with the glucose and produces an absorption in the optical band dependent on the amount of glucose present and which participates in the reaction. In addition to the expense of manufacturing such reagent based systems, these assays may be interfered with by other blood constituents that reduce their accuracy and reproducibility.
Although reagent-based optical assays have been successfully produced and commercialized, blood absorption characteristics in the infrared (IR) region of the electromagnetic spectrum have been recently explored to measure blood glucose concentrations. Using IR absorption characteristics has advantages over reagent-based optical measurements since glucose exhibits significant absorption in several IR wavelength regions without the need to perform a reaction with another chemical species that must be added to the blood sample.
However, other chemical species including water, alanine, albumin, hemoglobin, urea, lactate and others also absorb strongly at several IR band frequencies. Some of these constituents are present in the blood at concentrations of 50 or 100 times or more than the glucose concentration. Because the sample absorption at any given wavelength is a sum of the absorptions of each component at that wavelength, IR absorption measurements are complicated by the presence of these other components. Consequently, methods that allow effective compensation and adjustments to measured IR absorption for the presence of other blood components would be beneficial to provide a low cost and accurate system for diabetics and others in need of periodic glucose monitoring.